Piezoelectricity is the ability of certain crystalline materials to develop an electrical charge proportional to an applied mechanical stress. The converse effect can also be seen in these materials where strain is developed proportional to an applied electrical field. The Curie's originally discovered it in the 1880's. Today, piezoelectric materials for industrial applications are lead based ceramics available in a wide range of properties. Piezoelectric materials are the most well known active material typically used for transducers as well as in adaptive structures.
Mechanical compression or tension on a poled piezoelectric ceramic element changes the dipole moment, creating a voltage. Compression along the direction of polarization, or tension perpendicular to the direction of polarization, generates voltage of the same polarity as the poling voltage. Tension along the direction of polarization, or compression perpendicular to the direction of polarization, generates a voltage with polarity opposite that of the poling voltage. These actions are generator actions—the ceramic element converts the mechanical energy of compression or tension into electrical energy. This behavior is used in fuel-igniting devices, solid state batteries, force-sensing devices, and other products. Values for compressive stress and the voltage (or field strength) generated by applying stress to a piezoelectric ceramic element are linearly proportional up to a material-specific stress. The same is true for applied voltage and generated strain.
The review article “Advances In Energy Harvesting Using Low Profile Piezoelectric Transducers” by Shashank Priya, published in J Electroceram (2007) 19:165-182 provides a comprehensive coverage of the recent developments in the area of piezoelectric energy harvesting using low profile transducers and provides the results for various energy harvesting prototype devices. A brief discussion is also presented on the selection of the piezoelectric materials for on and off resonance applications.
The paper “On Low-Frequency Electric Power Generation With PZT Ceramics” by Stephen R. Platt, Shane Farritor, and Hani Haider, published in IEEE/ASME Transactions On Mechatronics, VOL. 10, NO. 2, April 2005 discusses the potential application of PZT based generators for some remote applications such as in vivo sensors, embedded MEMS devices, and distributed networking. The paper points out that developing piezoelectric generators is challenging because of their poor source characteristics (high voltage, low current, high impedance) and relatively low power output.
The article “Energy Scavenging for Mobile and Wireless Electronics” by Joseph A. Paradiso and Thad Starner, published by the IEEE CS and IEEE ComSoc, 1536-1268/05 reviews the field of energy harvesting for powering ubiquitously deployed sensor networks and mobile electronics and describers systems that can scavenge power from human activity or derive limited energy from ambient heat, light, radio, or vibrations.
In the review paper “A Review of Power Harvesting from Vibration using Piezoelectric Materials” by Henry A. Sodano, Daniel J. Inman and Gyuhae Park published in The Shock and Vibration Digest, Vol. 36, No. 3, May 2004 197-205, Sage Publications discuses the process of acquiring the energy surrounding a system and converting it into usable electrical energy—termed power harvesting. The paper discuss the research that has been performed in the area of power harvesting and the future goals that must be achieved for power harvesting systems to find their way into everyday use.
Intl. Patent Application WO/07/038157A2 entitled “Energy Harvesting Using Frequency Rectification” to Carman Gregory P. and Lee Dong G.; filed: Sep. 21, 2006 discloses an energy harvesting apparatus for use in electrical system, having inverse frequency rectifier structured to receive mechanical energy at frequency, where force causes transducer to be subjected to another frequency.
U.S. Pat. No. 5,265,481 to Sonderegger, Hans C., et al. entitled “Force sensor systems especially for determining dynamically the axle load, speed, wheelbase and gross weight of vehicles” discloses sensor system incorporated in road surface—has modular configuration for matching different road widths.